ISTH/SSC lupus anticoagulant testing guidelines: how far have these been adopted by laboratories?

New method to differentiate between lupus anticoagulants, progressive coagulation inhibitors and coagulation factor deficiencies in the mixing tests

INTRODUCTION

Mixing tests in activated partial thromboplastin time (APTT) are used for the differentiation between lupus anticoagulants (LA), coagulation inhibitors, and factor deficient samples with APTT prolongation. However, the indexes for the differentiation have not been established. The present study aimed to develop new mixing test indexes for the differentiation.

METHODS

Twenty-six LA-positive, 8 progressive coagulation factor VIII inhibitor, and 35 coagulation deficient samples were employed. APTT were measured for normal plasma, patient plasma, and mixing plasma prepared at a ratio of 1:1 proportion in both without incubation and 2 h-incubation. New two parameters named as ALD50 and mixture plasma-patient plasma after Warming change rate Subtraction (WaS) calculated from the clotting times of normal, 1:1 mixing and patient samples with/without 2 h-incubation were established. In the samples with WaS result of <10.2%, ALD50 of ≥87.8%, and < 87.8% were defined as LA and coagulation factor deficiency, respectively, and WaS of ≥10.2% defined progressive coagulation factor inhibitors.

RESULTS

Sensitivity and specificity to LA were 80.8% and 93.0% for ALD50, and sensitivity and specificity to progressive coagulation factor inhibitor were 100.0% and 100.0% for WaS, respectively. The agreement between sample classification and WaS-ALD50 was 88.4% (61/69).

CONCLUSIONS

ALD50 and WaS showed acceptable sensitivity and specificity to LA and progressive coagulation factor inhibitor, respectively. These indexes would be useful for the differentiation between LA, factor deficiency, and progressive coagulation factor inhibitor in the mixing tests.

How to Achieve Standardization? Diluted Russell Viper Venom Test for Lupus Anticoagulant Detection in a Chinese Female Population

On an international scale, guidelines and proposals for lupus anticoagulant detection have been published over the last 20 years, but until now, standardization has not been completely realized. The aim of this study was to evaluate the different ways of interpreting the results of lupus anticoagulant detection for standardization. A retrospective review of 15 447 instances of lupus anticoagulant detection by the diluted Russell Viper Venom test for female patients presenting with problems relating to the areas of reproduction, gynecology and obstetrics was performed. Lupus anticoagulant data were compared between different departments, months, reagent lots and cutoffs. Significant differences were found in patient data between different reagent lots, especially between lots of screening reagents (monthly average: highest 37.96 s vs lowest 33.88 s) and in the positive rates of lupus anticoagulant by different detection cutoffs (47.58% by using LA1/LA2 > 1.20 without normalization as a cutoff in Lot 1 vs 1.52% by using LA1 > 44 s as a cutoff in Lot 3). Compared with the cutoff using the value above the 99th percentile of LA1 for the healthy donors per lot, the cutoff using integrated tests with normalization had the smaller deviation of positive rate between different reagent lots. Pregnant women had higher LA1/LA2 levels than nonpregnant women. Based on the results, normalization is needed because there are significant lot-to-lot variations. Integrated tests with normalization might be a better standard by which to confirm lupus anticoagulant. Pregnant women should have population-specific cutoffs because they have higher LA1/LA2 levels.

Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis: Update of the guidelines for lupus anticoagulant detection and interpretation

This guidance focuses on methodological aspects of lupus anticoagulant (LA) testing, as well as interpretation of results for clinicians. The main changes in how to test for LA compared with the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee 2009 guidelines, in the preanalytical phase are more detailed recommendations on how to handle testing in anticoagulated patients, and the timing of testing. Also, routine coagulation tests are advised to obtain more information on the coagulation background of the patient, and when necessary, anti-Xa activity measurement for heparins or specific assays for direct oral anticoagulants should be performed. The three-step procedure with two test systems (diluted Russell's viper venom time and activated partial thromboplastin time [aPTT]) is essentially not changed. Silica remains the preferable activator in the aPTT assays, but ellagic acid is not excluded. We advise simultaneous performance of the mixing and confirmatory step, in each sample with a prolonged screening test. The confirmatory step can also be performed on a mixture of patient plasma and normal pooled plasma. Cutoff values should be established in-house on at least 120 normals, with transference of the manufacturer's cutoffs as an alternative. Reporting of results has not been changed, although more attention is focused on what clinicians should know. Patient selection for LA testing has been expanded.

Ruling out lupus anticoagulants with mixing test-specific cutoff assessment and the index of circulating anticoagulant

BACKGROUND

Lupus anticoagulant (LA) is classified in the antibody family that is recognized in antiphospholipid syndrome. Mixing tests are recommended for LA detection, and either a mixing test-specific cutoff (MTC) or index of circulating anticoagulant (ICA) is used for the interpretation. Although we previously showed MTC had higher sensitivity for LA than ICA, there are few studies investigating specificity.

OBJECTIVES

To investigate specificity of multiple activated partial thromboplastin time (APTT) and diluted Russell's viper venom time (dRVVT) reagents for inhibitors using plasmas with non-LA causes of prolonged clotting times, interpreted with MTC and ICA.

METHODS

Seventy-six factor-deficient samples (either artificially prepared, hereditary deficiency, or warfarin), and 12 inhibitors (either coagulation factor inhibitors, rivaroxaban, or apixaban) were used. Samples were tested with 4 APTTs, 1 dilute APTT (dAPTT), and 2 dRVVT reagents, and all elevated screen ratios were followed up with mixing tests. Frequencies of corrected and not-corrected results were calculated.

RESULTS

The frequency of MTC and ICA corrected results, suggesting factor deficiency, were 5% to 43% and 79% to 100%, respectively, except for dAPTT, where MTC and ICA performed similarly. Frequencies of MTC and ICA not-corrected results, suggesting inhibition, were 29% to 100% and 25% to 67%, respectively.

CONCLUSIONS

The data indicate that MTC has a tendency to generate not-corrected mixing tests in factor-deficient, warfarin, and other inhibitor samples, while ICA exhibited higher specificity. When we perform the mixing test and interpret the data, it is important to understand the characteristics of the indexes for maximizing the diagnostic potential of mixing test.

Newly developed dilute Russell's viper venom reagents for lupus anticoagulant detection with improved specificity

Background Dilute Russell's viper venom time (dRVVT) is indispensible in lupus anticoagulant (LA) detection yet commercial reagents from different suppliers perform variably, no gold standard assays exist and therapeutic anticoagulation interference is problematic. Objective The objective of this study was to compare a new formulation dRVVT with two currently available dRVVTs. Materials and methods Life Diagnostics (LD) dRVVT and Stago PTT-LA were routinely used for lupus anticoagulant detection, plus Taipan snake venom time/ecarin time (TSVT/ET) for patients on warfarin or rivaroxaban. Siemens dRVVT and the new HYPHEN BioMed (HBM) dRVVT were tested with 193 patient samples. Group 1, 59 non-anticoagulated patients (NAPs) LA-positive in LD dRVVT; Group 2, 15 PTT-LA-positive/dRVVT-negative NAPs; Group 3, 24 LA-positive warfarinized patients; Group 4, 13 patients on rivaroxaban; Group 5, 62 LA-negative thrombotic NAPs; Group 6, 20 warfarinized, non-antiphospholipid syndrome patients. Results Accepting that the Life Diagnostics reagents were acting as a pseudo-gold standard, Siemens dRVVT detected 56/59, (95%) Group 1 LA and HBM dRVVT 46/59, (76%), one each from Group 2, and Siemens dRVVT detected one in Group 5. The lower HBM dRVVT detection rate mainly concerned weaker LA, where between-reagent concordance is problematic. All Group 3 patients appeared LA-positive in undiluted plasma with Siemens dRVVT, as did 16/24 (67%) with HBM dRVVT but the fewer LA-positives in mixing tests better mapped to clear LA-positives with LD dRVVT. LD and Siemens dRVVTs exhibited 87% and 95% false-positivity for Group 6 whilst HBM dRVVT had none. Increasing the cut-off improved accuracy. Applying higher cut-offs improved accuracy in Group 4 patients. Conclusion HBM dRVVT exhibited improved specificity, mainly due to less interference by anticoagulation, but reduced sensitivity, compared to the other dRVVTs employed.

Anti-phospholipid syndrome: Current opinion on mechanisms involved, laboratory characterization and diagnostic aspects

Anti-phospholipid syndrome is a complex and severe clinical situation, associated with symptoms such as recurrent thrombosis, arterial or venous, at any site, pregnancy loss, and other related syndromes. These clinical burdens, are highly variable from patient to patient, and are associated with biological abnormalities, such as the presence of the Lupus Anticoagulant or phospholipid dependent antibodies, confirmed on two occasions at least 12 weeks apart. From the diagnosis standpoint, both, functional (clotting) or immunological assays, are difficult to standardize and to optimize, due to the absence of reference material, or a characteristic clinical group, and international reference preparations. Large cohort studies are necessary for defining the usefulness of each assay, in terms of specificity, sensitivity, accuracy and for following-up the disease evolution. Clotting assays are based on Activated Partial Thromboplastin Time (APTT) and diluted Russell Viper Venom Time (dRVVT), performed at low and high phospholipid concentration, or on 1:1 mixtures of tested sample and a normal plasma pool. They allow evaluation of the paradoxal effects of LAs, which are pro-thrombotic in vivo, and anticoagulant in vivo. Use of synthetic phospholipids improves assay specificities and sensitivities, especially in patients treated with anticoagulants. Immunoassays can also be used for testing phospholipid dependent antibodies, first identified and measured as anti-cardiolipin antibodies, but now characterized as targeted to phospholipid cofactor proteins: mainly β2GP1 (which exposes cryptic epitopes upon binding to phospholipids), and in some cases prothrombin, and more rarely Protein S, Factor XIII, Protein Z or Annexin V. Use of optimized assays designed with well-characterized anionic phospholipids, then complexed with highly purified phospholipid cofactor protein (mainly β2GP1), offers a better link between reactivity and clinical associations, than the former assays which were empirically designed with cardiolipin. Standardization also remains complicated due to the absence of international standards and harmonized quantitation units. Validation on large cohorts of negative and positive patients remains the key approach for defining assay performance and clinical usefulness. Laboratory practice for all these methods is now greatly facilitated thanks to the use of automated instruments and dedicated software. Along with clinical criteria, laboratory assays are of great usefulness for identification and confirmation of the anti-phospholipid syndrome and they allow disease follow-up when appropriate patient management is in place.

Application of different lupus anticoagulant diagnostic algorithms to the same assay data leads to interpretive discrepancies in some samples

BACKGROUND

Gold standard lupus anticoagulant (LA) assays and reference plasmas do not exist and detection is based on inference in a medley of coagulation assays, creating potential for interpretive discrepancies when applying different algorithms.

OBJECTIVES

To investigate discrepancies from applying different algorithms to a common data set.

METHODS

Diagnostic data on 311 non-anticoagulated patients LA-positive by dilute Russell's viper venom time (dRVVT) and/or dilute activated partial thromboplastin time (dAPTT) assays were employed to compare algorithms. Routine testing applied interpretive criteria from guidelines endorsing classification as LA-positive despite negative mixing tests, after exclusion of other clotting abnormalities. Integrated testing without mixing tests, and the classical algorithm where negative mixing tests preclude confirm tests, were then retrospectively applied to those data.

RESULTS

Initial testing showed 92/311 (29.6%) were LA-positive by dRVVT only, 156/311 (50.1%) by dAPTT only, and 63/311 (20.3%) by both assays. All dAPTT-positive plasmas remained positive with integrated testing but eight dRVVT-positives became negative. Other data suggested they were false-negatives. The classical algorithm altered 52/155 (33.5%) dRVVT and 111/219 (50.7%) dAPTT interpretations to LA-negative because of normal mixing tests, most of which were apparently weak LA in undiluted plasma.

CONCLUSIONS

The classical algorithm improves diagnostic specificity and confidence but risks missing some genuine LA due to false-negative mixing tests. Integrated testing can be diagnostically accurate and logistically efficient but oversimplifies complex cases. Performing mix and confirm in response to an elevated screen with their interpretation based on clinical data, coagulation screens and the LA-assay design offers a potentially valuable option.

Overview of Hemostasis and Thrombosis and Contribution of Laboratory Testing to Diagnosis and Management of Hemostasis and Thrombosis Disorders

Hemostasis is a complex and tightly regulated process whereby the body attempts to maintain a homeostatic balance to permit normal blood flow, without bleeding or thrombosis. When this balance is disrupted, due to trauma or underlying congenital bleeding or thrombotic disorders, clinical intervention may be required. To assist clinicians in diagnosing and managing affected patients, hemostasis laboratories offer an arsenal of tests, both routine (screening) and more specialized (diagnostic). In general, screening assays are used to screen for hemostasis-related disease or to monitor or measure the effect of anticoagulant therapy, which may be applied to treat patients with recent thrombosis or at risk of thrombosis. Diagnostic assays are used to diagnose or exclude specific hemostasis-related diseases, and in some cases, to monitor or measure the effect of anticoagulant therapy, or alternatively procoagulant therapy that may be applied to those at risk of bleeding. This chapter provides an overview of hemostasis and thrombosis with respect to laboratory tests that may be applied to affected patients.

Presence of Antiphospholipid Antibodies as a Risk Factor for Thrombotic Events in Patients with Connective Tissue Diseases and Idiopathic Thrombocytopenic Purpura

OBJECTIVE

Antiphospholipid syndrome (APS) is a well-known complication of habitual abortion and/or thrombosis and is frequently associated with autoimmune diseases.

METHODS

We retrospectively investigated the relationships between the presence of antiphospholipid antibodies (aPLs) and the incidence of thrombotic events (THEs) in 147 patients with various connective tissue diseases (CTD) suspected of having APS and 86 patients with idiopathic thrombocytopenic purpura (ITP). THEs were observed in 41 patients, including 14 cases of venous thrombosis, 21 cases of arterial thrombosis and eight cases of complications of pregnancy.

RESULTS

The prevalence of THE was significantly high in the systemic lupus erythematosus (SLE) patients compared with the other CTD patients and ITP patients. The frequency of lupus anticoagulant (LA), anticardiolipin antibodies (aCL)-β2-glycoprotein (GPI) complex IgG and aPL was significantly high in the SLE patients compared with the ITP patients. Subsequently, the rate of development of THE was significantly high in the patients with aPLs. In particular, the incidence of THE was significantly high in the SLE or ITP patients with LA, aCL-β2GPI IgG or aPL. The optimal cut-off values for LA, aCL IgG and aCL-β2GPI complex IgG for the risk of THEs were higher in the SLE patients in comparison to the values obtained when using the kit provided by the manufacturer.

CONCLUSION

Although aPLs is frequently associated with SLE and is a causative factor for thrombosis, the optimal cut-off value for aPL for predicting the occurrence of THEs varies among different underlying diseases.

Antiphospholipid antibody testing and standardization

The laboratory criteria that define patients with antiphospholipid syndrome (APS) include lupus anticoagulant (LAC), anticardiolipin antibodies and anti-β2 glycoprotein I antibodies (aβ2GPI). All assays show methodological shortcomings and the combination of the three tests, each with different sensitivity and specificity, and hence, differences in clinical utility make the laboratory diagnosis of APS challenging. Consensus guidelines and proposals for antiphospholipid antibodies (aPL) testing have been published in the last 20 years and have led to a substantial improvement. Despite efforts so far, standardization is not reached yet, but progress has been made. On-going efforts to reduce the interlaboratory/interassay variations remain important; even an absolute standardization cannot be feasibly achieved. Taking into account the methodological shortcomings of the means we have available, more detailed guidelines may help in adequate performance of aPL testing. This review will focus on the efforts and achievements in standardization and on the weaknesses and strengths of the current available laboratory methods.

Direct Thrombin Inhibitors and Factor Xa Inhibitors Can Influence the Diluted Prothrombin Time Used as the Initial Screen for Lupus Anticoagulant

Context.—Lupus anticoagulant (LA) is a heterogeneous group of antiphospholipid antibodies. Among others, diluted prothrombin time (dPT) is a sensitive screening test for LA; however, the interpretation of LA tests is difficult in patients treated with anticoagulants. The effect of different types of anticoagulants on the result of LA tests, particularly on dPT, has not been studied extensively.

Objective.—To determine whether the direct thrombin inhibitors lepirudin and argatroban and the predominantly factor Xa inhibitors enoxaparin, danaparoid, and fondaparinux could interfere with LA screening based on dPT.

Design.—Each drug was added to normal and LA-positive plasmas in clinically relevant concentrations. Each sample was tested for dPT. Samples with factor Xa inhibitors were investigated before and after addition of heparinase. Mixing and confirmatory tests for LA were not performed.

Results.—In the presence of lepirudin or argatroban, dPT increased notably and the dPT ratio exceeded the cutoff value even at subtherapeutic concentrations resulting in false positivity. With increasing factor Xa inhibitor concentrations, a linear increase of dPT ratios and false-positive results were also demonstrated. Although heparinase could almost completely neutralize the anti-Xa effect of all investigated factor Xa inhibitors, dPT ratio returned to the basal level only in case of enoxaparin.

Conclusions.—Here we provide evidence that both the direct thrombin and indirect factor Xa inhibitors influence dPT assay for LA, causing false positivity. This should be considered when interpreting LA results during anticoagulant therapy. However, dPT seems to be a reliable test for LA screening under enoxaparin therapy after neutralization by heparinase.

Presence of antiphospholipid antibody is a risk factor in thrombotic events in patients with antiphospholipid syndrome or relevant diseases

Antiphospholipid antibodies (aPL) including lupus anticoagulant (LA), anticardiolipin antibodies (aCL) IgG and aCL-β2-glycoprotein I (β2GPI) complex IG are causative factors for thrombotic event (THE). We retrospectively investigated relationships between aPLs and THE in 458 patients suspected of having antiphospholipid syndrome. THEs were observed in 232 of 458 patients, including 148 cases of venous thrombosis, 59 of arterial thrombosis, 18 of microthrombosis, and 20 of complications of pregnancy. The frequency of THE was significantly high in patients positive for LA and/or aPL. In patients with autoimmune disease (AID), the frequency of THE was significantly high in patients with any types of aPLs. Additionally, risk of THE was significantly increased in patients with more than two types of aPLs. Prolonged activated partial thromboplastin time indicated a high risk for THE. However, neither thrombocytopenia nor AID was a risk for THE. In conclusion, the presence of aPL is an indicator for high risk of THE in patients in whom THE was suspected. However, the risk of THE in aPL-positive patients varied among patients with different underlying diseases.

APTT reagent with ellagic acid as activator shows adequate lupus anticoagulant sensitivity in comparison to silica-based reagent

BACKGROUND

Lupus anticoagulant (LA) is an antibody that interferes with phospholipid-dependent coagulation reactions. Activated partial thromboplastin time (APTT) is widely used as a test for LA screening. APTT reagents are composed of activators, such as silica or ellagic acid, and phospholipids, and APTT reagents with silica are recommended for LA screening because of greater sensitivity. However, the effects of activators on LA activity have not been adequately investigated.

OBJECTIVES

In this study, we examined whether an ellagic acid-based reagent was highly sensitive to LA in a low phospholipid condition and useful for LA screening.

METHODS

Silica-based (SL) and ellagic acid-based (EA) reagents were prepared in-house with the same composition and concentration of phospholipids, while the commercial APTT reagents APTT-SLA (SLA), Actin FSL (FSL), APTT-SP (SP) and PTT-LA (PTT) were also included in the study.

RESULTS

The normal reference ranges for SL and EA were 30.1-47.0 and 28.0-40.2 s, respectively, while the cut-off index values for circulating anticoagulant activity (ICA) calculated from the results obtained with SL, EA, SLA, FSL, SP and PTT were 12.9, 11.5, 13.2, 15.6, 14.3 and 14.0, respectively. The sensitivity of those reagents based on those cut-off values was 91%, 96%, 68%, 46%, 91% and 86%, respectively.

CONCLUSIONS

Our results showed that the ellagic acid-based reagent was more sensitive to LA than silica-based reagents in a low phospholipid condition and had adequate sensitivity to detect LA. We concluded that the sensitivity of APTT reagents for LA is dependent on phospholipid concentration and not the activator.

Laboratory diagnosis of the lupus anticoagulant

Lupus anticoagulants are autoantibodies that are associated with an increased risk of thromboembolic events and adverse pregnancy outcomes. They are identified by a systematic, laboratory-based approach that includes the following steps: 1) prolongation of a phospholipid-dependent screening assay, 2) demonstration of an inhibitory activity by mixing studies with healthy pooled plasma, and 3) documentation that the inhibitory activity is phospholipid dependent. Laboratory testing can be complicated by several variables, however, including preanalytical factors, multiple reagents and testing platforms, and difficulties with interpreting the results. Guidelines have been developed through several professional organizations that build upon the steps listed above and provide guidance to improve the reproducibility of test results. This article reviews the guidelines developed by the Lupus Anticoagulant/Phospholipid Dependent Antibodies Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis and addresses several common issues encountered during testing for these clinically relevant autoantibodies.